I have the same problem - ping & traceroute is ok, host list loads but no host replies... win 7x64, no firewall, no problem in other games (udp working fine).
if i join race from lfsworld in browser, it connects and stays forever with message "waiting for guest info".
what to check next?
UPDATE: my problem was probably Killer networks E2200 ethernet - after last driver update (Killer e2200 PCI-E Gigabit Ethernet Controller NDIS 6.20 - v.8.0.2.42) LFS is working.